Hydraulic retarder control system

Abstract

The hydraulic retarder control system comprises pressure reducing valves which can switch the pressure of the air to be supplied from a pressure air source 4 to an air/liquid conversion device 25 at least to a low pressure, an intermediate pressure and a high pressure, or a proportional electromagnetic valve 110 which can reduce and adjust the pressure of the air in a stageless manner, and running speed detect devices 100, 111 which detect the fact that the running speed of a vehicle is equal to or slower than a given running speed. When there is given a detect signal by the running speed detect devices 100, 111, then the pressure reducing valves 32, 95 or the proportional electromagnetic valve 110 are or is switched over to a pressure higher than a set pressure for running speeds exceeding the given running speed, so that the high pressure air from the pressure air source 4 can be supplied to the air/liquid conversion device 25.

What is claimed is: 
     
       1. A hydraulic retarder control system, comprising: a hydraulic retarder mounted on a rotary shaft rotatable together with a vehicle wheel comprising a rotor and an unrotatable stator, said hydraulic retarder being always filled with operation liquid;   a clutch device drivable by a drive device for connecting or disconnecting said rotor with or from said rotary shaft;   a closed circuit for connecting the operation liquid inlet and outlet of said hydraulic retarder;   an air/liquid conversion device for applying an air pressure to said operation liquid present in said closed circuit;   pressure reducing means capable of switching the pressure of the air to be supplied from a pressure air source to said air/liquid conversion device; and   running speed detect means for detecting the fact that the running speed of a vehicle is equal to or slower than a given running speed,   wherein, when there is given a detect signal by said running speed detect means, then the pressure of said pressure reducing means is switched into a higher pressure condition than a set pressure at running speeds exceeding said given running speed, so that a high pressure air from said pressure air source can be supplied to said air/liquid conversion device.   
     
     
       2. A hydraulic retarder control system as set forth in claim 1, wherein said pressure reducing means comprises a first pressure reducing valve for reducing the pressure of the air to be supplied from said pressure air source to said air/liquid conversion device to a low pressure, a second pressure reducing valve for reducing the pressure of said air to an intermediate pressure, a low speed pressure reducing valve for reducing the pressure of said air to a high pressure, and switch valves each having a low pressure position, an intermediate pressure position or a high pressure position for switching the pressure of said air to be supplied to said air/liquid conversion device through said first and second and low speed pressure reducing valves, whereby, when there is given a detect signal by said running speed detect means while said switch valves are allowed to take said intermediate position, said pressure reducing means allows said switch valves to take said high pressure position, so that said high pressure air from said pressure air source can be supplied to said air/liquid conversion device. 
     
     
       3. A hydraulic retarder control system as set forth in claim 1, wherein said pressure reducing means comprises a proportional electromagnetic valve capable of linearly reducing the pressure of said air to be supplied from said pressure air source to said air/liquid conversion device, whereby, when said running speed detect means detects a condition that the running speed of said vehicle is equal to or slower than said given running speed, then said proportional electromagnetic valve is controlled on the basis of a control value to be set in accordance with said detect signal of said running speed detect means to thereby increase gradually the pressure of said air to be supplied to said air/liquid conversion device as said running speed is lowered.